Heat-curing epoxy resin composition containing non-aromatic ureas as accelerator

ABSTRACT

The present invention relates to heat-curing epoxy resin compositions, which are characterized by high impact strength, good storage stability, and a low curing temperature. The epoxy resin compositions are suitable for use as a construction shell adhesive and for producing structural foams. They can already be cured in so-called bottom-baking conditions. Furthermore, it has been found that the use of an accelerator of the formula (Ia) or (Ib) results in an increase of the impact strength of heat-curing epoxy resin compositions.

TECHNICAL FIELD

The invention relates to the field of heat-curing epoxy resincompositions, more particularly of high-impact heat-curing epoxy resincompositions, more particularly for use as bodyshell adhesive and forproducing structural foams.

PRIOR ART

Heat-curing epoxies are long-established resin compositions. For sometime now attempts have been undertaken to eliminate or at least greatlyreduce the great disadvantage of epoxy resin compositions, namely theirbrittleness, which leads to the cured epoxy resin composition, understress, acquiring cracks or suffering destruction. This has already beentried by adding impact modifiers or through chemical modification ofepoxy resins.

One important field of use for heat-curing epoxy resin compositions isin vehicle construction, and more particularly in the adhesive bondingor foam filling of cavities in bodyshell construction. In both cases,after the epoxy resin composition has been applied, the body is heatedin a cathodic dipcoating oven, in an operation which also cures and,where appropriate, foams the heat-curing epoxy resin composition.

Rapid curing is enabled through the use, routinely, of accelerants inaddition to heat-activable hardeners for epoxy resins. One importantcategory of accelerants are ureas. High-impact heat-curing epoxy resincompositions which may include ureas as accelerants are known fromWO-A-20041055092, WO-A-2005/007720, and WO-A-2007/003650, for example.

In the market at present, however, efforts are in train to lower thetemperature of the cathodic dipcoating ovens. Hence within the marketthere is a great need for heat-curing epoxy resin compositions whichcure even at relatively low temperatures, in other words at atemperature of 150 to 170° C., after just a short time, typically 10 to15 minutes. Consequently, aromatic ureas are used which by virtue oftheir structure are significantly more reactive. Nevertheless, it hasbeen found that the use of aromatic accelerants of this kind leads togreat problems with the storage stability of the heat-curing epoxy resincompositions.

SUMMARY OF THE INVENTION

It is an object of the present invention, therefore, to provideheat-curing epoxy resin compositions, more particularly high-impactheat-curing epoxy resin compositions, which on the one hand have goodstorage stability at room temperature and on the other hand exhibitrapid curing at temperatures of 170° C. to 160° C., typically at 165° C.

This object has been achieved, surprisingly, by means of a heat-curingepoxy resin composition in accordance with claim 1. This epoxy resincomposition can be used to particularly good effect as a one-componentheat-curing adhesive, more particularly as a heat-curing one-componentbodyshell adhesive in vehicle construction, and also for producingcoatings, more particularly paints, and also for producing a structuralfoam for the reinforcement of cavities, more particularly of metallicstructures.

Entirely surprisingly it has also been found that the use of anaccelerant of the formula (Ia) or (Ib) leads to an increase in theimpact toughness of heat-curing epoxy resin compositions. This applieseven in the case of those heat-curing epoxy resin compositions whichalready possess a considerable degree of impact toughness (measured, forexample, as the impact strength to ISO 11343).

Other aspects of the invention are subject matter of other independentclaims. Particularly preferred embodiments of the invention are subjectmatter of the dependent claims.

EMBODIMENTS OF THE INVENTION

The present invention relates to heat-curing epoxy resin compositionswhich comprise

-   -   a) at least one epoxy resin A having on average more than one        epoxide group per molecule;    -   b) at least one epoxy-resin hardener B which is activated by        elevated temperature and is an amine, amide, carboxylic        anhydride or polyphenol; and    -   c) at least one accelerant C of the formula (Ia) or (Ib)

In formula (Ia) for the accelerant C, R¹ is H or an n-valent aliphatic,cycloaliphatic or araliphatic radical.

Additionally, R² and R³

either

-   -   each independently of one another are an alkyl group or aralkyl        group;

or

-   -   together are a divalent aliphatic radical having 3 to 20 C atoms        which is part of an optionally substituted heterocyclic ring        having 5 to 8, preferably 6, ring atoms.

Finally, n is from 1 to 4, more particularly 1 or 2.

In formula (Ib) for the accelerant C, R^(1′) is an n′-valent aliphatic,cycloaliphatic or araliphatic radical.

R^(2′) is an alkyl group or aralkyl group or alkylene group.

R^(3′) independently at each occurrence is H or an alkyl group oraralkyl group.

Finally, n′ is from 1 to 4, more particularly 1 or 2.

The term “independently of one another” or “independently at eachoccurrence” in the definition of groups and radicals means that two ormore groups which occur that are referred to identically in the formulamay in each case have different definitions.

An “araliphatic radical” is understood in this document to be an aralkylgroup, i.e., an alkyl group which is substituted by aryl groups (cf.Römpp, CD Römpp Chemie Lexikon, Version 1, Stuttgart/New York, GeorgThieme Verlag 1995).

It is essential to the invention that, if R¹ is not H, R¹ is an n-valentaliphatic, cycloaliphatic or araliphatic radical and is not an aromaticor heteroaromatic radical. In other words, the accelerant C inparticular does not have the formula (I′).

It is also essential that, if R^(3′) is not H, R^(3′) is not an aromaticor heteroaromatic radical, i.e., the accelerant C in particular does nothave the formula (I″).

where Z¹ and Z² are H or any desired organic radical.

It has been found that accelerants with aromatic radicals R¹ are notstorage-stable—that is, they increase the viscosity of heat-curing epoxyresin compositions within a short time, to a degree which is no longernegligible as far as the handling of the composition is concerned.

R¹ is more particularly a radical of an aliphatic, cycloaliphatic oraraliphatic mono-, di-, tri- or tetraisocyanate of the formula (III),after removal of the n Isocyanate groups.

R¹[NCO]_(n)   (III)

This mono-, di-, tri- or tetraisocyanate of the formula (III) is eithera monomeric mono-, di-, tri- or tetraisocyanate or a dimer or oligomerof one or more monomeric di- or triisocyanates, with dimers or oligomersbeing more particularly biurets, isocyanurates, and uretdiones.

Suitable monomeric monoisocyanates are alkyl isocyanates, such as, forexample, butyl isocyanate, pentyl isocyanate, hexyl isocyanate, octylisocyanate, decyl isocyanate, and dodecyl isocyanate, and alsocyclohexyl isocyanate, methylcyclohexyl isocyanate, and benzylisocyanate.

Particularly suitable monomeric diisocyanates are 1,4-butanediisocyanate, hexamethylene diisocyanate (HDI), isophorone diisocyanate(IPDI), trimethylhexamethylene diisocyanate (TMDI), 2,5- or2,6-bis(isocyanatomethyl)bicyclo[2.2.1 ]heptane, dicyclohexylmethyldiisocyanate (H₁₂MDI), m-tetramethylxylylene diisocyanate (TMXDI), andm-xylylene diisocyanate (XDI) and hydrogenated m-xylylene diisocyanate(H₈XDI).

Particularly suitable dimers or oligomers are HDI biuret, HDIisocyanurate, IPDI biuret, IPDI isocyanurate, HDI diuretdione, IPDIisocyanurate.

Dimers or oligomers of this kind are available commercially, forexample, as Desmodur N-100 (Bayer), Luxate HDB 9000 (Lyondell), DesmodurN-3300 (Bayer), Desmodur N-3600 (Bayer), Luxate HT 2000 (Lyondell),Desmodur N-3400 (Bayer), Luxate HD 100 (Lyondell), Desmodur Z 4470(Bayer), Vestanat T 1890/100 (Hüls) or Luxate IT 1070 (Lyondell).

Of course, suitable mixtures of the stated di- or triisocyanates canalso be used.

R¹ is more particularly

alternatively

-   -   an alkylene group having 4 to 10 carbon atoms, more particularly        a hexamethylene group,

or is

or

-   -   is a biuret or an isocyanurate of an aliphatic or araliphatic        diisocyanate, following removal of the isocyanate groups;

or

-   -   is a xylylene group, more particularly a m-xylylene group.

Particular preferred as R¹ is HDI, IPDI, HDI biuret, and XDI, followingremoval of the NCO groups.

R² and R³ particularly suitably together form a butylene, pentamethyleneor hexamethylene group, preferably a pentamethylene group.

Preferably, R² and R³ independently of one another are each an alkylgroup having from 1 to 5 carbon atoms, more particularly eachindependently of one another a methyl, ethyl or propyl group, preferablyeach a methyl group.

R¹ in one embodiment is H. This is preferred in the case where R² and R³independently of one another are each a methyl, ethyl or propyl group,preferably each a methyl group.

R¹ with particular preference is an n-valent aliphatic, cycloaliphaticor araliphatic radical.

R^(1′) is first more particularly a diamine which is selected from thegroup consisting of 1,4-diaminobutane, hexamethylenediamine,isophoronediamine, trimethylhexamethylenediamine, 2,5- or2,6-bis(aminomethyl)bicyclo[2.2.1]-heptane, dicyclohexylmethyldiamine,m-tetramethylxylylenediamine, and m-xylylenediamine, hydrogenatedm-xylylenediamine, ethylenediamine, 1,3-propanediamine, and1,2-propanediame, after the removal of the two amino groups.

R^(2′) is first more particularly a C₁-C₁₀ alkyl radical or an aralkylradical having 7 to 20 C atoms, preferably a methyl, ethyl, propyl,butyl or pentyl group.

R^(1′) is secondly more particularly an ethylene, propylene, butylene,methylethylene or 1,2-dimethylethylene group.

R^(2′) is secondly more particularly an ethylene, propylene, butylene,methylethylene or 1,2-dimethylethylene group.

The two alkylene groups R^(1′) and R^(2′), together with the ureanitrogen atoms, form a ring, more particularly piperazine or2,3,5,6-tetramethylpiperazine or homopiperazine (1,4-diazacycloheptane).

R^(3′) is more particularly a monomeric monoisocyanate which is selectedfrom the group consisting of butyl isocyanate, pentyl isocyanate, hexylisocyanate, octyl isocyanate, decyl isocyanate, and dodecyl isocyanate,and also cyclohexyl isocyanate, methylcyclohexyl isocyanate, and benzylisocyanate.

The accelerants C of the formula (Ia) are readily accessiblesynthetically from the reaction of an aliphatic, cycloaliphatic oraraliphatic mono-, di-, tri- or tetraisocyanate of the formula (III)with a secondary amine of the formula (IV).

In a second variant of the synthesis, the accelerant C of the formula(Ia) is prepared from the reaction of a primary aliphatic,cycloaliphatic or araliphatic amine of the formula (V) and of a compoundof the formula (VI).

Latter variant is advantageous more particularly when polyisocyanates ofthe formula (III) are unavailable or difficult to obtain commercially.

The accelerants C of the formula (Ib) are readily accessiblesynthetically from the reaction of an aliphatic, cycloaliphatic oraraliphatic monoisocyanate of the formula (IIIa) with a secondary amineof the formula (IVa) or (IVb).

In formula (IVb) x′ and y′ each independently of one another are 1, 2,3, 4 or 5 and the substituents Q^(1′), Q^(2′), Q^(3′), and Q^(4′) areindependently of one another each H or a C₁— to C₅ alkyl group.Preferably x′ and y′ are 1 or 2, preferably each 1; in other words, thesecondary amine of the formula (IVb) is preferably piperazine or2,3,5,6-tetramethylpiperazine or homopiperazine (1,4-diazacycloheptane),more preferably piperazine or 2,3,5,6-tetramethylpiperazine.

The secondary amines of the formula (IVa) may be prepared in their turn,more particularly, easily from the alkylation of primary amines of theformula R^(1′)[NH₂]_(n′).

Particularly preferred amines of the formula (IVa) are selected from thegroup consisting of N,N′-dimethyl-1,2-diaminocyclohexane,N,N′-dimethylethylenediamine, N,N-dimethyl-1,3-propanediamine,bis-isopropylated IPDA (Jefflink 754 (Huntsman)),N,N′-diisobutylethylenediamine, and N-ethyl-N′-methylethylenediamine.

The accelerant C has more particularly a molecule of less than 1000g/mol, more particularly between 80 and 800 g/mol. If the molecularweight is greater, the accelerant effect is reduced and the amountrequired for use is significantly higher, a factor which in turn maylead to poorer mechanical properties.

The amount of accelerant C is advantageously 0.01%-6.0%, moreparticularly 0.02%-4.0%, preferably 0.02%-2.0%, by weight, based on theweight of the epoxy resin A.

The heat-curing epoxy resin composition further comprises at least oneepoxy resin A having on average more than on epoxide group per molecule.The epoxide group takes the form preferably of a glycidyl ether group.The epoxy resin A having on average more than one epoxide group permolecule is preferably a liquid epoxy resin or a solid epoxy resin. Theterm “solid epoxy resin” is very well known to a person skilled in theepoxide art and is used in contrast to “liquid epoxy resins”, The glasstransition temperature of solid resins is above room temperature—thatmeans they can be comminuted to pourable particles at room temperature.

Preferred solid epoxy resins have the formula (A-I)

In this formula the substituents R′ and R″ independently of one anotherare either H or CH₃.

Moreover, the index s is >1.5, more particularly from 2 to 12.

Solid epoxy resins of this kind are available commercially, for example,from Dow or Huntsman or Hexion.

Compounds of the formula (A-I) with an index s of between 1 and 1.5 arereferred to by the person skilled in the art as semisolid epoxy resins.For the purposes of the present invention they are considered likewiseto be solid resins. Preference, however, is given to epoxy resins in thenarrower sense, in other words where the index a has a value of >1.5.

Preferred liquid epoxy resins have the formula (A-II)

In this formula the substituents R′″ and R″″ independently of oneanother are either H or CH₃. Moreover, the index r is from 0 to 1.Preferably r is less than 0.2.

The resins in question are therefore, preferably, diglycidyl ethers ofbisphenol A (DGEBA), of bisphenol F, and of bisphenol-A/F (thedesignation “A/F” refers here to a mixture of acetone with formaldehyde,used as a reactant in its preparation). Liquid resins of this kind areavailable, for example, as Araldite® GY 250, Araldite® PY 304, Araldite®GY 282 (Huntsman) or D.E.R.™ 331 or D.E.R.™ 330 (Dow) or Epikote 828(Hexion).

The epoxy resin A is preferably a liquid epoxy resin of the formula(A-II). In an even more preferred embodiment, the heat-curing epoxyresin composition comprises not only at least one liquid epoxy resin ofthe formula (A-II) but also at least one solid epoxy resin of theformula (A-I).

The fraction of epoxy resin A is preferably 10%-85%, more particularlypreferably 15%-70%, preferably 15%-60%, by weight, of the weight of thecomposition.

The heat-curing epoxy resin composition further comprises at least oneepoxy-resin hardener B which is activated by elevated temperature and isan amine, amide, carboxylic anhydride or polyphenol.

Amines are considered to include amines in quaternary form such as, forexample, boron halide-ammonium salts of amines.

Hardeners of this kind are very well known to a person skilled in theart. Preferred amines are biguanides or 3,3′- or 4.4′-diaminodiphenolsulfone or mixtures thereof. Preferred amides are the dihydrazides ofadipic acid or sebacic acid. Preferred carboxylic anhydrides arepyromellitic dianhydride or the salts of pyromellitic dianhydride withimidazoles, of the kind available commercially, for example, asVestagon® B55 from Degussa; trimellitic anhydride or derivatives ortrimellitic anhydride, of the kind available commercially, for example,as Aradur® 3380 from Huntsman. Preferred polyphenols are phenolnovolaksor cresol novolaks, of the kind available commercially, for example, asAradur® 3082 from Huntsman.

More particularly the hardener in question is one of the hardeners Bwhich is selected from the group consisting of diaminodiphenol sulfone,adipic dihydrazide, derivatives of trimellitic anhydride, novolaks, anddicyandiamide.

The most preferred hardener B is dicyandiamide.

The amount of the epoxy resin hardener B which is activated by elevatedtemperature is advantageously 0.1%-30%, more particularly 0.2%-10%, byweight, based on the weight of the epoxy resin A.

The heat-curing epoxy resin composition further comprises preferably atleast one toughness improver D.

By a “toughness improver” is meant, in this document, an addition to anepoxy resin matrix that added even at low levels of 0.1%-50%, moreparticularly 0.5%-40%, by weight, produces a significant increase intoughness and is therefore capable of accommodating higher flexural,tensile, impact or jolting stress before the matrix tears or ruptures.

The toughness improver D may be a solid or a liquid toughness improver.

In a first embodiment, solid toughness improvers are organic,ion-exchanged laminar minerals. Toughness improvers of this kind aredescribed in U.S. Pat. No. 5,707,439 or in U.S. Pat. No. 6,197,849, forexample. Particularly suitable solid toughness improvers of this kindare known to a person skilled in the art by the term organoclay ornanoclay and are available commercially, for example, under the groupnames Tixogel® or Nanofil® (Südchemie), Cloisite® (Southern ClayProducts) or Nanomer® (Nanocor Inc.) or Garamite® (Southern ClayProducts).

In a second embodiment, solid toughness improvers are block copolymersThe block copolymer is obtained, for example, from an anionic orcontrolled free-radical polymerization of methacrylic ester with atleast one other monomer containing an olefinic double bond. Preferredmonomers containing an olefinic double bond are more particularly thosein which the double bond is conjugated directly with a heteroatom orwith at least one further double bond. Suitable more particularly arethose monomers selected from the group encompassing styrene, butadiene,acrylonitrile, and vinyl acetate. Preference is given to to acrylicester/styrene/acrylonitrile copolymers (ASA), obtainable, for example,under the name GELOY 1020 from GE Plastics.

Particularly preferred block copolymers are block copolymers of methylmethacrylate, styrene, and butadiene. Block copolymers of this kind areavailable, for example, as triblock copolymers under the groupdesignation SBM from Arkema.

In a third embodiment, solid toughness improvers are core-shellpolymers. Core-shell polymers are composed of an elastic core polymerand a rigid shell polymer. Particularly suitable core-shell polymers arecomposed of a core of elastic acrylate polymer or butadiene polymer,surrounded by a rigid shell of a rigid thermoplastic polymer. Thiscore-shell structure either forms spontaneously by separation of a blockcopolymer, or is imposed by the polymerization regime as a latex orsuspension polymerization with subsequent grafting. Preferred core-shellpolymers are so-called MBS polymers, which are available commerciallyunder the tradename Clearstrength™ from Atofina, Paraloid™ from Rohm andHaas or F-351™ from Zeon.

Particular preference is given to core-shell polymer particles alreadyin the form of a dried polymer latex. Examples thereof are GENIOPERLM23A from Wacker, with polysiloxane core and acrylate shell,radiation-crosslinked rubber particles of the NEP series, produced byEliokem, or Nanoprene from Lanxess or Paraloid EXL from Rohm and Haas.

Further comparable examples of core-shell polymers are offered under thename Albidur™ by Nanoresins AG, Germany.

In a fourth embodiment, solid toughness improvers are solid reactionproducts of a solid carboxylated nitrile rubber with excess epoxy resin.

Liquid toughness improvers are preferably liquid rubbers or liquidtoughness improvers based on a polyurethane polymer.

In a first embodiment the liquid rubber is an acrylonitrile/butadienecopolymer which is terminated with carboxyl groups or (meth)acrylategroups or epoxide groups, or is a derivative thereof.

Liquid rubbers of this kind are available commercially, for example,under the name Hycar® CTBN and CTBNX and ETBN from Nanoresins AG,Germany. Suitable derivatives are more particularly elastomer-modifiedpolymers containing epoxide groups, of the kind sold commercially underthe product line Polydis®, preferably from the product line Polydis® 36. . . , from Struktol® (Schill+Seilacher Group, Germany) or under theproduct line Albipox (Nanoresins, Germany).

In a second embodiment this liquid rubber is a liquid polyacrylaterubber which is fully miscible with liquid epoxy resins and whichseparates to form microdroplets only when the epoxy resin matrix iscured. Liquid polyacrylate rubbers of this kind are available, forexample, under the designation 20208-XPA from Rohm and Haas.

In a third embodiment this liquid rubber is a polyether amide which isterminated with carboxyl groups or epoxide groups. Polyamides of thiskind are prepared more particularly from the reaction ofamino-terminated polyethylene ether or polypropylene ether, of the kindsold, for example, under the name Jeffamine® by Huntsman, withdicarboxylic anhydride, and subsequent reaction with epoxy resins, ofthe kind described. for example, in example 15 in conjunction withexample 13 of DE 2123033. Instead of dicarboxylic anhydride it is alsopossible to use hydroxybenzoic acid or hydroxybenzoates.

To a person skilled in the art it is clear that, of course, mixtures ofliquid rubbers can also be used, more particularly mixtures of carboxyl-or epoxide-terminated acrylonitrile/butadiene copolymers or ofderivatives thereof.

The toughness improver D is preferably selected from the groupconsisting of blocked polyurethane polymers, liquid rubbers, epoxyresin-modified liquid rubbers, and core-shell polymers.

In one preferred embodiment the toughness improver D is a blockedpolyurethane polymer of the formula (II).

In this formula m and m′ are each between 0 and 8, with the proviso thatm+m′ is from 2 to 8.

Moreover, Y¹ is a linear or branched polyurethane polymer PU1 terminatedwith m+m′ isocyanate groups, following the removal of all of theterminal isocyanate groups.

Y² is independently at each occurrence a blocking group which iseliminated at a temperature above 100° C.

Y³ is independently at each occurrence a group of the formula (II′).

In this formula R⁴ first is a radical of an aliphatic, cycloaliphatic,aromatic or araliphatic epoxide which contains a primary or secondaryhydroxyl group, following the removal of the hydroxide and epoxidegroups, and p is 1, 2 or 3.

Y² is more particularly, independently at each occurrence, a substituentwhich is selected from the group consisting of

In these groups, R⁵, R⁶, R⁷, and R⁸ are each independently of oneanother an alkyl or cycloalkyl or aralkyl or arylalkyl group or else R⁵together with R⁶, or R⁷ together with R⁸, forms part of a 4- to7-membered ring which if desired is substituted.

Furthermore, R⁹, R^(9′), and R¹⁰ each independently of one another is analkyl or aralkyl or arylalkyl group or is an alkyloxy or aryloxy oraralkyloxy group, and R¹¹ is an alkyl group.

R¹³ and R¹⁴ are each independently of one another an alkylene grouphaving 2 to 5 C atoms which optionally has double bonds or issubstituted, or are a phenylene group or are a hydrogenated phenylenegroup, and R¹⁵, R¹⁶, and R¹⁷ are each independently of one another H oran alkyl group or an aryl group or an aralkyl group.

Finally, R¹⁸ is an aralkyl group or is a mono- or polycyclic substitutedor unsubstituted aromatic group which optionally contains aromatichydroxyl groups.

The dashed lines in the formulae in this document represent in each casethe bond between the substituent in question and the associated moleculeremainder.

Considered as R¹⁸ are, in particular, first phenols or bisphenolsfollowing removal of a hydroxyl group. Preferred examples of suchphenols and bisphenols are, in particular, phenol, cresol, resorcinol,pyrocatechol, cardanol (3-pentadecenylphenol (from Cashew Nut ShellOil)), nonylphenol, phenols reacted with styrene or withdicyclopentadiene, bisphenol A, bisphenol F, and 2,2′-diallylbisphenolA.

Also considered as R¹⁸ are, in particular, hydroxybenzyl alcohol andbenzyl alcohol following removal of a hydroxyl group.

If R⁵, R⁶, R⁷, R⁸, R⁹, R^(9′), R¹⁰, R¹¹, R¹⁵, R¹⁶ or R¹⁷ is an alkylgroup, it is more particularly a linear or branched C₁-C₂₀ alkyl group.

If R⁵, R⁶, R⁷, R⁸, R⁹, R^(9′), R¹⁰, R¹⁵, R¹⁶, R¹⁷ or R¹⁸ is an aralkylgroup, said group is more particularly a methylene-bonded aromaticgroup, more particularly a benzyl group.

If R⁵, R⁶, R⁷, R⁸, R⁹, R^(9′) or R¹⁰ is an alkylaryl group, then it ismore particularly a phenylene-attached C₁ to C₂₀ alkyl group, such astolyl or xylyl, for example.

Particularly preferred radicals Y² are radicals which are selected fromthe group consisting of

The radical Y here is a saturated or olefinically unsaturatedhydrocarbon radical having 1 to 20 C atoms, more particularly having 1to 15 C atoms. Preferred Ys are more particularly allyl, methyl, nonyl,dodecyl or an unsaturated C₁₅ alkyl radical having 1 to 3 double bonds.

The radical X is H or is an alkyl, aryl or aralkyl group, moreparticularly H or methyl.

The indices z′ and z″ are 0, 1, 2, 3, 4 or 5, with the proviso that thesum z′+z″ is between 1 and 5.

The blocked polyurethane polymer of the formula (II) is prepared fromthe isocyanate group-terminated linear or branched polyurethane polymerPU1 with one or more isocyanate-reactive compounds Y²H and/or Y³H. Iftwo or more such isocyanate-reactive compounds are used, the reactionmay take place sequentially or with a mixture of these compounds.

The reaction takes place such that the one or more isocyanate-reactivecompounds Y²H and/or Y³H are used stoichiometrically or instoichiometric excess in order to ensure that all of the NCO groups arereacted.

The isocyanate-reactive compounds Y³H is a monohydroxyl epoxide compoundof the formula (IIIa).

If two or more such monohydroxyl epoxide compounds are used, thereaction may take place sequentially or may take place with a mixture ofthese compounds.

The monohydroxyl epoxide compound of the formula (IIIa) has 1, 2 or 3epoxide groups. The hydroxyl group of this monohydroxyl epoxide compound(IIIa) may represent a primary or a secondary hydroxyl group.

Monohydroxyl epoxide compounds of this kind can be produced, forexample, by reacting polyols with epichlorohydrin. Depending on reactionregime, the reaction of polyfunctional alcohols with epichlorohydrinalso produces the corresponding monohydroxyl epoxide compounds, asby-products, in different concentrations. These compounds can beisolated by means of typical separating procedures. Generally speaking,however, it is sufficient to use the product mixture which is obtainedin the glycidylation reaction of polyols and which is composed of polyolhaving undergone full reaction and partial reaction to form the glycidylether. Examples of such hydroxyl-containing epoxides are butanediolmonoglycidyl ether (present in butanediol diglycidyl ether), hexanediolmonoglycidyl ether (present in hexanediol diglycidyl ether),cyclohexanedimethanol glycidyl ether, trimethylolpropane diglycidylether (present as a mixture in trimethylolpropane triglycidyl ether),glycerol diglycidyl ether (present as a mixture in glycerol triglycidylether), pentaerythritol triglycidyl ether (present as a mixture inpentaerythritol tetraglycidyl ether). Preference is given to usingtrimethylolpropane diglycidyl ether, which occurs in a relatively highfraction in customarily prepared trimethylolpropane triglycidyl ether.

Use may also be made, however, of other, similar hydroxyl-containingepoxides, more particularly glycidol, 3-glycidyloxybenzyl alcohol orhydroxymethylcyclohexene oxide. Additionally preferred is the β-hydroxyether of the formula (IIIb), which is present at about 15% in commercialliquid epoxy resins prepared from bisphenol A (R═CH₃) andepichlorohydrin, and also the corresponding β-hydroxy ethers of theformula (IIIb) that are formed in the reaction of bisphenol F (R═H) orof the mixture of bisphenol A and bisphenol F with epichlorohydrin.

Additionally preferred are also distillation residues which are obtainedduring the preparation of high-purity distilled liquid epoxy resins.These distillation residues have an up to three times higherconcentration of hydroxyl-containing epoxides than do commercialundistilled liquid epoxy resins. Moreover, a wide variety of epoxideswith a β-hydroxy ether group, prepared by reacting (poly)epoxides with adeficit amount of monofunctional nucleophiles such as carboxylic acids,phenols, thiols or secondary amines, can also be used,

The radical R⁴ is with more particular preference a trivalent radical ofthe formula

where R is methyl or H.

The free primary or secondary OH functionality of the monohydroxylepoxide compound of the formula (IIIa) allows efficient reaction withterminal isocyanate groups of polymers, without the need to usedisproportionate excesses of the epoxide component.

The polyurethane polymer PU1 on which Y′ is based can be prepared fromat least one diisocyanate or triisocyanate and also from at least onepolymer Q_(PM) having terminal amino, thiol or hydroxyl groups and/orfrom an optionally substituted polyphenol Q_(PP).

Throughout the present specification the prefix “poly” in“polyisocyanate”, “polyol”, “polyphenol”, and “polymercaptan” designatesmolecules which formally contain two or more of the respectivefunctional groups.

Suitable diisocyanates are for example aliphatic, cycloaliphatic,aromatic or araliphatic diisocyanates, more particularly commerciallycustomary products such as methylenediphenyl diisocyanate (MDI),1,4-butane diisocyanate, hexamethylene diisocyanate (HDI), toluenediisocyanate (TDI), tolidine diisocyanate (TODI), isophoronediisocyanate (IPDI), trimethylhexamethylene diisocyanate (TMDI), 2,5- or2,6-bis(isocyanatomethyl)bicyclo[2.2.1]heptane, 1,5-naphthalenediisocyanate (NDI), dicyclohexylmethyl diisocyanate (H₁₂MDI),p-phenylene diisocyanate (PPDI), m-tetramethylxylylene diisocyanate(TMXDI), etc. and also their dimers. Preference is given to HDI, IPDI,MDI or TDI.

Suitable triisocyanates are for example timers or biurets of aliphatic,cycloaliphatic, aromatic or araliphatic diisocyanates, more particularlythe isocyanurates and biurets of the diisocyanates described in thepreceding paragraph.

Suitable mixtures of di- or triisocyanates can of course also be used.

Most particular suitability as polymers Q_(PM) having terminal amino,thiol or hydroxyl groups is possessed by polymers Q_(PM) having two orthree terminal amino, thiol or hydroxyl groups.

The polymers Q_(PM) advantageously have an equivalent weight of300-6000, more particularly of 600-4000, preferably of 700-2200g/equivalent of NCO— reactive groups.

Suitability as polymers Q_(PM) is possessed by polyols, examples beingthe following commercially customary polyols or any desired mixturesthereof:

-   -   polyoxyalkylene polyols, also called polyether polyols, which        are the polymerization product of ethylene oxide, 1,2-propylene        oxide, oxetane, 1,2- or 2,3-butylene oxide, tetrahydrofuran or        mixtures thereof, optionally polymerized by means of a starter        molecule having two or three active H atoms such as water, for        example, or compounds having two or three OH groups. Use may be        made both of polyoxyalkylene polyols which have a low degree of        unsaturation (measured by ASTM D-2849-69 and reported in        milliequivalents of unsaturation per gram of polyol (meq/g)),        prepared for example with the aid of what are called double        metal cyanide complex catalysts (DMC catalysts for short), and        of polyoxyalkylene polyols having a higher degree of        unsaturation, prepared for example by means of anionic catalysts        such as NaOH, KOH or alkali metal alkoxides. Of especial        suitability are polyoxypropylene diols and triols having a        degree of unsaturation of less than 0.02 meq/g and having a        molecular weight in the range of 1000-30 000 daltons,        polyoxybutylene diols and triols, polyoxypropylene diols and        triols having a molecular weight of 400-8000 daltons, and also        “EO-endcapped” (ethylene oxide-endcapped) polyoxypropylene diols        or triols. The latter are specific        polyoxypropylene-polyoxyethylene polyols which are obtained, for        example, by alkoxylating pure polyoxypropylene polyols with        ethylene oxide when the polypropoxylation is finished, and which        as a result contain primary hydroxyl groups.    -   hydroxy-terminated polybutadiene polyols, such as those, for        example, prepared by polymerization of 1,3-butadiene and allyl        alcohol or by oxidation of polybutadiene, and also their        hydrogenation products;    -   styrene-acrylonitrile grafted polyether polyols, of the kind        supplied, for example, by Elastogran under the name Lupranol®;    -   polyhydroxy-terminated acrylonitrile/butadiene copolymers, of        the kind preparable, for example, from carboxyl-terminated        acrylonitrile/butadiene copolymers (available commercially under        the name Hycar® CTBN from Nanoresins AG, Germany) and epoxides        or amino alcohols;    -   polyester polyols, prepared, for example, from dihydric to        trihydric alcohols such as, for example, 1,2-ethanediol,        diethylene glycol, 1,2-propanediol, dipropylene glycol,        1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentyl        glycol, glycerol, 1,1,1-trimethylolpropane or mixtures of the        aforementioned alcohols, with organic dicarboxylic acids or        their anhydrides or esters, such as, for example, succinic acid,        glutaric acid, adipic acid, suberic acid, sebacic acid,        dodecanedicarboxylic acid, maleic acid, fumaric acid, phthalic        acid, isophthalic acid, terephthalic acid, and hexahydrophthalic        acid or mixtures of the aforementioned acids, and also polyester        polyols from lactones such as s-caprolactone, for example;    -   polycarbonate polyols, of the kind obtainable through reaction,        for example, of the abovementioned alcohols—those used for        synthesizing the polyester polyols with dialkyl carbonates,        diaryl carbonates or phosgene.

Advantageous polymers Q_(PM) are those of polyols with a functionalityof two or more which have OH equivalent weights of 300 to 6000 g/OHequivalent, more particularly of 600 to 4000 g/OH equivalent, preferably700-2200 g/OH equivalent. Also advantageously the polyols are selectedfrom the group consisting of polyethylene glycols, polypropyleneglycols, polyethylene glycol-polypropylene glycol block copolymers,polybutylene glycols, hydroxyl-terminated polybutadienes,hydroxyl-terminated butadieneacrylonitrile copolymers,hydroxyl-terminated synthetic rubbers, their hydrogenation products, andmixtures of these stated polyols.

It is also possible, furthermore, as polymers Q_(PM), to usedifunctional or higher-functional amino-terminated polyethylene ethers,polypropylene ethers of the kind sold, for example, under the nameJeffamine® by Huntsman, polybutylene ethers, polybutadienes,butadiene/acrylonitrile copolymers, of the kind sold, for example, underthe name Hycar® ATBN from Nanoresins AG, Germany, and also furtheramino-terminated synthetic rubbers or mixtures of the stated components.

For certain applications, suitable polymers Q_(PM) include moreparticularly hydroxyl-containing polybutadienes or polyisoprenes ortheir partially or fully hydrogenated reaction products.

It is additionally possible for the polymers Q_(PM) also to have beenchain-extended in a way which can be carried out, in a manner known tothe person skilled in the art, through the reaction of polyamines,polyols, and polyisocyanates, more particularly of diamines, diols, anddiisocyanates.

Taking the example of a diisocyanate and a diol, and depending on thechosen stoichiometry, the product of said reaction, as shown below, is aspecies of the formula (A) or (B)

The radicals Q¹ and Q² are a divalent organic radical and the indices uand v vary, depending on stoichiometric ratio, from 1 to typically 5.

These species of the formula (A) or (B) can then in turn be reactedfurther. Thus, for example, from the species of the formula (A) and adiol having a divalent organic radical Q³ it is possible to form achain-extended polyurethane polymer PU1 of the following formula:

From the species of the formula (B) and a diisocyanate having a divalentorganic radical Q⁴ it is possible to form a chain-extended polyurethanepolymer PU1 of the following formula:

The indices x and y vary, depending on stoichiometric ratio, from 1 totypically 5, and more particularly are 1 or 2.

Furthermore, the species of the formula (A) can also be reacted with thespecies of the formula (B), giving a chain-extended polyurethane polymerPU1 containing NCO groups.

For the chain extension more particular preference is given to diolsand/or diamines and diisocyanates. It is of course clear to the personskilled in the art that polyols of higher functionality, such astrimethylolpropane or pentaerythritol, or polyisocyanates of higherfunctionality, such as isocyanurates of diisocyanates, can also be usedfor the chain extension.

In the case of the polyurethane polymers PU1 generally, and in the caseof the chain-extended polyurethane polymers specifically, it shouldadvantageously be ensured that the polymers do not have excessively highviscosities, particularly if compounds of relatively high functionalityare used for the chain extension, since high viscosities may hampertheir reaction to form the polymers of the formula (II) and/or mayhamper the application of the composition.

Preferred polymers Q_(PM) are polyols having molecular weights between600 and 6000 daltons, selected from the group consisting of polyethyleneglycols, polypropylene glycols, polyethylene glycol-polypropylene glycolblock polymers, polybutylene glycols, hydroxyl-terminatedpolybutadienes, hydroxyl-terminated butadiene-acrylonitrile copolymers,and mixtures thereof. Particularly preferred polymers Q_(PM) areα,ω-dihydroxypolyalkylene glycols having C₂-C₆ alkylene groups or havingmixed C₂-C₆ alkylene groups and terminated with amino groups, thiolgroups or, preferably, hydroxyl groups. Particularly preferred arepolypropylene glycols or polybutylene glycols. Additionally particularlypreferred are hydroxyl-group-terminated polyoxybutylenes.

Particularly suitable as polyphenol Q_(PP) are bis-, tris-, andtetraphenols. By these are meant not only pure phenols but also, whereappropriate, substituted phenols. The nature of the substitution may bevery diverse. The reference here is more particularly to substitutiondirectly on the aromatic nucleus to which the phenolic OH group isattached. By phenols are meant, furthermore, not only mononucleararomatics, but also polynuclear or fused aromatics or heteroaromaticswhich contain the phenolic OH group directly on the aromatic orheteroaromatic moiety, respectively.

The nature and position of such a substituent exerts an influenceon—among other things—the reaction with isocyanates that is necessaryfor the formation of the polyurethane polymer PU1.

Particularly suitable are the bis- and trisphenols. Examples of suitablebisphenols or trisphenols include 1,4-dihydroxybenzene,1,3-dihydroxybenzene, 1,2-dihydroxybenzene, 1,3-dihydroxytoluene,3,5-dihydroxybenzoates, 2,2-bis(4-hydroxyphenyl)propane (=bisphenol A),bis(4-hydroxyphenyl)methane (=bisphenol F), bis(4-hydroxyphenyl)sulfone(=bisphenol S), naphthoresorcinol, dihydroxynaphthalene,dihydroxyanthraquinone, dihydroxybiphenyl,3,3-bis(p-hydroxyphenyl)phthalides,5,5-bis(4-hydroxyphenyl)hexahydro-4,7-methanoindane, phenolphthalein,fluoroscein,4,4′-[bis(hydroxyphenyl)-1,3-phenylenebis(1-methylethylidene)](=bisphenol M),4,4′-[bis(hydroxyphenyl)-1,4-phenylenebis(1-methylethylidene)](=bisphenol P), 2,2′-diallylbisphenol A, diphenols and dicresolsprepared by reacting phenols or cresols with diisopropylidenebenzene,phloroglucinol, gallic esters, phenol novolaks or cresol novolaks withOH functionality of 2.0 to 3.5, and also all isomers of theaforementioned compounds.

Preferred diphenols and dicresols prepared by reacting phenols orcresols with diisopropylidenebenzene have a chemical structural formulaof the kind shown below, correspondingly, for cresol as an example:

Particular preference is given to bisphenols of low volatility. The mostpreferred are bisphenol M, bisphenol S, and 2,2′-diallylbisphenol A.

Preferably the Q_(PP) contains 2 or 3 phenolic groups.

In a first embodiment the polyurethane polymer PU1 is prepared from atleast one diisocyanate or triisocyanate and also from a polymer Q_(PM)having terminal amino, thiol or hydroxyl groups. The polyurethanepolymer PU1 is prepared in a manner known to the person skilled in thepolyurethane art, more particularly by using the diisocyanate ortriisocyanate in a stoichiometric excess in relation to the amino, thiolor hydroxyl groups of the polymer Q_(PM).

In a second embodiment the polyurethane polymer PU1 is prepared from atleast one diisocyanate or triisocyanate and also from an optionallysubstituted polyphenol Q_(PP). The polyurethane polymer PU1 is preparedin a manner known to the person skilled in the polyurethane art, moreparticularly by using the diisocyanate or triisocyanate in astoichiometric excess in relation to the phenolic groups of thepolyphenol Q_(PP).

In a third embodiment the polyurethane polymer PU1 is prepared from atleast one diisocyanate or triisocyanate and also from a polymer Q_(PM)having terminal amino, thiol or hydroxyl groups and also from anoptionally substituted polyphenol Q_(PP). For the preparation of thepolyurethane polymer PU1 from at least one diisocyanate or triisocyanateand also from a polymer Q_(PM) having terminal amino, thiol or hydroxylgroups and/or from an optionally substituted polyphenol Q_(PP) there arevarious possibilities available.

In a first process, called “one-pot process”, a mixture of at least onepolyphenol Q_(PP) and at least one polymer Q_(PM) is reacted with atleast one diisocyanate or triisocyanate in an isocyanate excess.

In a second process, called “2-step process I”, at least one polyphenolQ_(PP)is reacted with at least one diisocyanate or triisocyanate in anisocyanate excess and then with at least one polymer Q_(PM) in asubstoichiometric amount.

In the third process finally, called “2-step process II”, at least onepolymer Q_(PM) is reacted with at least one diisocyanate ortriisocyanate in an isocyanate excess and then with at least onepolyphenol Q_(PP) in a substoichiometric amount.

The three processes lead to isocyanate-terminated polyurethane polymersPU1 which, while having the same composition, may differ in the sequenceof their constituent units. All three processes are suitable, but the“two-step process II” is preferred.

Where the above-described isocyanate-terminal polyurethane polymers PU1are synthesized from difunctional components, it has been found that thepolymer Q_(PM)/polyphenol Q_(PP) equivalent ratio is preferably greaterthan 1.50 and the polyisocyanate/(polyphenol Q_(PP)+polymer Q_(PM))equivalent ratio is preferably greater than 1.20.

Where the average functionality of the components used is greater than2, the increase in molecular weight is more rapid than in the purelydifunctional case. For the person skilled in the art it is clear thatthe limits on the possible equivalent ratios depend greatly on whetherthe chosen polymer Q_(PM), the polyphenol Q_(PP), the polyisocyanate, ortwo or more of the stated components possess a functionality >2.Accordingly it is possible to set different equivalent ratios, whoselimits are determined by the viscosity of the resulting polymers andwhich must be determined experimentally from one case to the next.

The polyurethane polymer PU1 is preferably elastic in character anddisplays a glass transition temperature Tg of less than 0° C.

The terminally blocked polyurethane polymer of the formula (II) isadvantageously elastic in character and, furthermore, is advantageouslysoluble or dispersible in liquid epoxy resins.

In the formula (II) m is preferably other than 0.

Particularly preferred are at the same time two or more toughnessimprovers D as a constituent of the heat-curing epoxy resin composition.With particular preference the heat-curing epoxy resin compositioncomprises at least one blocked polyurethane polymer of the formula (II)and also at least one core-shell polymer and/or one carboxyl- or(meth)acrylate- or epoxide-group-terminated acrylonitrile/butadienecopolymer, or a derivative thereof.

The fraction of the toughness improver D is advantageously 0.1%-50%,more particularly 0.5%-30%, by weight, of the weight of the composition.

In one further preferred embodiment, the composition further comprisesat least one filler F. Fillers in question here are preferably carbonblack, mica, talc, kaolin, wollastonite, feldspar, syenite, chlorite,bentonite, montmorillonite, calcium carbonate (precipitated or ground),dolomite, quartz, silicas (fumed or precipitated), cristobalite, calciumoxide, aluminum hydroxide, magnesium oxide, hollow ceramic beads, hollowglass beads, hollow organic beads, glass beads, and color pigments.Reference to filler F is not only to the organically coated forms butalso to the uncoated commercially available forms and the forms known tothe person skilled in the art.

The total fraction of the overall filler F is advantageously 2%-50%,preferably 3%-35%, by weight, more particularly 5%-25% by weight basedon the weight of the overall composition.

In another preferred embodiment the composition comprises a chemicalblowing agent H, of the kind obtainable, for example, under thetradename Expancel™ from Akzo Nobel or Celogen™ from Chemtura orLuvopor™ from Lehmann & Voss, Germany. The fraction of the blowing agentH is advantageously 0.1%-3% by weight, based on the weight of thecomposition.

In one further preferred embodiment, the composition further comprisesat least one reactive diluent G which carries epoxide groups. Thesereactive diluents G are more particularly:

-   -   glycidyl ethers of monofunctional saturated or unsaturated,        branched or unbranched, cyclic or open-chain C₄-C₃₀ alcohols,        e.g., butanol glycidyl ether, hexanol glycidyl ether,        2-ethylhexanol ether, allyl glycidyl ether, tetrahydrofurfuryl        and furfuryl glycidyl ethers, trimethoxysilyl glycidyl ether,        etc.    -   glycidyl ethers of difunctional saturated or unsaturated,        branched or unbranched, cyclic or open-chain C₂-C₃₀ alcohols,        e.g., ethylene glycol, butanediol, hexanediol, and octanediol        glycidyl ethers, cyclohexanedimethanol diglycidyl ether,        neopentyl glycol diglycidyl ether, etc.    -   glycidyl ethers of trifunctional or polyfunctional, saturated or        unsaturated, branched or unbranched, cyclic or open-chain        alcohols such as epoxidized castor oil, epoxidized        trimethylolpropane, epoxidized pentaerythritol or polyglycidyl        ethers of aliphatic polyols such as sorbitol, glycerol,        trimethylolpropane, etc.    -   glycidyl ethers of phenol compounds and aniline compounds, such        as phenyl glycidyl ether, cresol glycidyl ether,        p-tert-butylphenyl glycidyl ether, nonylphenol glycidyl ether,        3-n-pentadecenyl glycidyl ether (from cashew nut shell oil),        N,N-diglycidylaniline, etc.    -   epoxidized amines such as N,N-diglycidylcyclohexylamine, etc.    -   epoxidized monocarboxylic or dicarboxylic acids such as glycidyl        neodecanoate, glycidyl methacrylate, glycidyl benzoate,        diglycidyl phthalate, tetrahydrophthalate, and        hexahydrophthalate, diglycidyl esters of dimeric fatty acids,        etc.    -   epoxidized difunctional or trifunctional polyether polyols of        low to high molecular mass, such as polyethylene glycol        diglycidyl ether, polypropylene glycol diglycidyl ether, etc.

Particular preference is given to hexanediol diglycidyl ether, cresylglycidyl-ether, p-tert-butylphenyl glycidyl ether, polypropylene glycoldiglycidyl ether, and polyethylene glycol diglycidyl ether.

The total fraction of the reactive diluent G carrying epoxide groups isadvantageously 0.1%-20%, preferably 0.5%-8%, by weight, based on theweight of the overall composition.

The composition may comprise further ingredients, more particularlycatalysts, heat stabilizers and/or light stabilizers, thixotropicagents, plasticizers, solvents, organic or mineral fillers, blowingagents, and dyes and pigments.

It has been found advantageous that the heat-curing epoxy resincomposition is free from organic carboxylic acids.

It has emerged that the heat-curing epoxy resin compositions of theinvention are especially suitable for use as one-component adhesives.The invention, in a further aspect, accordingly provides for the use ofthe above-described heat-curing epoxy resin composition as aone-component heat-curing adhesive, more particularly as a one-componentheat-curing body shell adhesive in vehicle construction. A one-componentadhesive of this kind has broad possibilities for use. In particular, itis possible therewith to realize heat-curing one-component adhesiveswhich are distinguished by a high impact toughness. Such adhesives arerequired for the bonding of heat-stable materials. By heat-stablematerials are meant materials which are dimensionally stable, at leastduring the cure time, at a curing temperature of 100-220° C., preferably120-200° C. These materials are more particularly metals and plasticssuch as ABS, polyamide, polyphenylene ether, composite materials such asSMC, unsaturated polyester GRP, composite epoxide materials or compositeacrylate materials. Preference is given to the application wherein atleast one material is a metal. A particularly preferred use is theadhesive bonding of like or different materials, more particularly inbodyshell construction in the automobile industry. The preferred metalsare principally steel, more particularly electrolytically galvanized,hot-dip galvanized, and oiled steel, Bonazinc-coated steel, andretrospectively phosphated steel, and also aluminum, more particularlyin the versions typically found in automaking.

With an adhesive based on a heat-curing composition of the invention itis possible to achieve the desired combination of high impact toughnesswith good storage stability and with low curing temperatures. Inaddition to these qualities the composition has high mechanical values.It has been found more particularly that glass transition temperaturesof above 85° C., in particular of 100° C. or more, can be achieved, thisbeing especially important for applications involving high workingtemperatures.

In another aspect, therefore, the invention provides a method ofadhesively bonding heat-stable materials, which involves contactingthese materials with an above-described epoxy resin composition, andwhich comprises one or more steps of curing at a temperature of 100-220°C., preferably 120-200° C. More particularly an adhesive of this kind isfirst contacted with the materials to be bonded, at a temperature ofbetween 10° C. and 80° C., more particularly between 10° C. and 60° C.,and is later cured at a temperature of typically 100-220° C., preferably120-200° C.

It has been found in particular that the heat-curing epoxy resincompositions can be cured even under what are called underbakeconditions, i.e., the composition achieves good mechanical curingproperties even at temperatures of below 170° C. It has become apparent,for example, that with compositions of this kind it is possible, byheating for 10 minutes at just 165° C., more particularly 160° C., toobtain tensile shear strength values (for details of the measurement,reference may be made here to the examples) of more than 15 MPa, moreparticularly of more than 19 MPa, and that these values differ onlyslightly from 30-minute 180° C-cured values.

Following adhesive bonding, the bonded materials may be used attemperatures between 120° C. and −40° C., preferably between 110° C. and−40° C., more particularly between 100° C. and −40° C.

A method of this kind for the bonding of heat-stable materials producesan adhesively bonded article, and this constitutes a further aspect ofthe present invention. An article of this kind is preferably a vehicleor a part for installation in or on a vehicle.

Of course, with a composition of the invention, it is possible, as wellas heat-curing adhesives, to realize sealants or coatings. Furthermore,the compositions of the invention are suitable not only for automakingbut also for other fields of application. Particularly noteworthy arerelated applications in the construction of means of transport such asboats, trucks, buses or rail vehicles, or in the construction ofconsumer goods such as washing machines, for example.

The heat-curing epoxy resin compositions described display preferablyexcellent mechanical properties, more particularly high tensilestrengths and high impact toughness, and also have excellent storagestability, even at a relatively long time at relatively hightemperatures, and nevertheless exhibit outstanding cure at temperaturesof 170° C. to 150° C., more particularly between 170° C. and 160° C.

It is possible, moreover, to obtain adhesives which possess a high glasstransition temperature, typically or more than 95° C.

Compositions can be formulated which typically have fracture energies,measured in accordance with ISO 11343, of more than 40 J, in some casesmore than 43 J, at 23° C.

One particularly preferred application of the heat-curing epoxy resincomposition of the invention is its application as a heat-curing bodyshell adhesive in vehicle construction.

It has emerged, moreover, that the heat-curing epoxy resin compositionsdescribed can be used for producing a structural foam for thereinforcement of cavities, especially of metallic structures. In thesecases the composition contains a chemical blowing agent H.

On heating, the chemical blowing agent first evolves a gas, and so,together with the composition, a foam is formed, and, secondly, theepoxy resin composition cures.

The at least partial filling of a cavity with a heat-curing compositionof this kind, and heating of the bonded materials to a temperature of100-220° C., preferably 120-200° C., produces a foamed article.

More particularly this produces a vehicle or vehicle component whichcomprises an article foamed in this way.

Entirely surprisingly it has further emerged that the use of anaccelerant of the formula (Ia) or (Ib), as described above, leads to anincrease in the impact toughness of heat-curing epoxy resincompositions. This is particularly also the case in heat-curing epoxyresin compositions which already possess a very high level of impacttoughness. Thus, for example, it has been possible, in heat-curing epoxyresin compositions which already have an impact peel strength ofapproximately 14 J, measured in accordance with ISO 11343 at 25° C., toachieve increases of more than 15%, and in certain cases even more than23%.

The reason this is particularly surprising is that aliphatic accelerantspossessing very similar structures, and occasionally even with the sameempirical formula, do not exhibit this effect. Aromatic accelerants notconforming to the formula (Ia) or (Ib), such as, for example,3,3′-(4-methyl-1,3-phenylene)bis(1,1-dimethylurea), do not display thiseffect to the same extent as the accelerants of the formula (Ia) or(Ib), and, moreover, result in a deterioration in storage stability.

EXAMPLES

Curing Agents for Epoxy Resins

N,N-Dimethylurea (=1,1-dimethylurea) (“asym DMH”)

-   n=1, R¹═H, R²═R³═CH₃

N,N-Dimethylurea was obtained from Aldrich, Switzerland.

N′,N′-Dimethyl-N-butylurea (=3-butyl-1,1-dimethylurea) (“BuDMH”)

-   n=1, R¹=n-butyl, R²═R³═CH₃

50 ml of tetrahydrofuran (THF) and 20.0 g of an approximately 33%strength solution of dimethylamine in ethanol (Fluka) (about 146 mmol ofamine) were charged to a 100 ml two-neck flask with reflux condenser.Subsequently, over 30 minutes, 14.5 g of butyl isocyanate (Fluka) (about146 mmol of NCO) were slowly added dropwise, producing a slightexothermic response. After 3 hours of stirring at ambient temperature,the solvent was stripped off on a rotary evaporator at 80° C. undervacuum. This gave about 21.0 g of a slightly yellowish, low-viscosityliquid. The desired adduct was used further without other purification.

Hexamethylenebis(1,1-dimethylurea)(=1,1′-(hexane-1,6-diyl)bis(3,3-dimethylurea) (“HDIDMH”)

-   n=2, R¹═—(CH₂)₆—, R²═R³═CH₃

50 ml of THF and 20.0 g of an approximately 33% strength solution ofdimethylamine in ethanol (Fluka) (about 146 mmol of amine) were chargedto a 100 ml two-neck flask with reflux condenser. Subsequently, over 30minutes, 10.0 g of hexamethylene diisocyanate (Fluka) (about 119 mmol ofNCO) were added slowly dropwise, producing a slight exothermic responseand immediately precipitating a white solid. After 2 hours of stirringat ambient temperature, the suspension was filtered. The filter productwas washed 3× with 20 ml of THF each time. The crude product obtainedwas dried under vacuum at 80° C. for 3 h. The desired product wasobtained in the form of 12.3 g of a white powder.

Adduct of Desmodur N-100 with dimethylurea (“N100DMH”)

-   n=3, R¹=formula (IX), R²═R³═CH₃

30 ml of THE and 20.0 g of an approximately 33% strength solution ofdimethylamine in ethanol (Fluka) (about 146 mmol of amine) were chargedto a 100 ml two-neck flask with reflux condenser. Subsequently, over 30minutes, 18.7 g of the hexamethylene diisocyanate trimer Desmodur N-100(Bayer) (about 118 mmol of NCO) in 20 ml of THF were slowly addeddropwise, producing a slight exothermic response. After 2 hours ofstirring at ambient temperature, the solvent and also the excessdimethylamine were evaporated first at 100° C. under a stream ofnitrogen and collected in a gas wash bottle with acidic water, followedby further drying on a rotary evaporator at 80° C. under vacuum.Decanting from the flask gave about 21.5 g of a virtually colorless,high-viscosity product. The desired adduct was used further withoutother purification.

Benzyldimethylurea (“BzDMH”)

-   n=1, R¹═—(CH₂)—C₆H₅, R²═R³═CH₃

15.0 g (139.5 mmol) of N,N-dimethylcarbamoyl chloride and 80 ml ofdioxane were charged to a 250 ml two-neck flask with reflux condenser.Subsequently 13.66 g (135 mmol) of triethylamine and 14.89 g (139 mmol)of benzylamine were added. After the exothermic response had subsided,the mixture was stirred at 90° C. for 5 h, during which there was rapidformation of a slightly orange suspension. The resulting suspension wasfiltered while hot. The turbidity which developed as the solution cooledwas removed by further filtration. The solvent was stripped off on arotary evaporator at 60° C. This gave above 14.0 g of a slightly orange,waxlike solid.

3,3′-(4-Methyl-1,3-phenylene)bis(1,1-dimethylurea) (“TDIDMH”)

-   n=2, R¹=formula (X), R²═R³═CH₃

3,3′-(4-Methyl-1,3-phenylene)bis(1,1-dimethylurea) was obtained fromFluka, Switzerland.

N,N′-Dimethylurea (=1,3-dimethylurea) (“sym DMH”)

-   n=1, R¹═CH₃, R²═H, R³═CH₃

N,N′-Dimethylurea was obtained from Fluka, Switzerland.

N,N,N′,N′-Tetramethylurea (=1,1,3,3-tetramethylurea) (“TMH”)

N,N,N′,N′-Tetramethylurea was obtained from Fluka, Switzerland.

TABLE 1 Raw materials used. D.E.R. 330 (Bisphenol A diglycidyl ether =“DGEBA”) Dow Polypox R7 (tert-butylphenyl glycidyl ether) = “Polypox”)UPPC Polydis 3614, epoxy-resin-modified CTBN (=“Polydis””) StruktolDicyandiamide (=“Dicy”) Degussa PolyTHF 2000 (difunctional polybutyleneglycol) BASF (OH equivalent weight = about 1000 g/OH equivalent)Liquiflex H (hydroxyl-terminated polybutadiene) Krahn (OH equivalentweight = about 1230 g/OH equivalent) Isophorone dicyanate (=“IPDI”)Evonik Cardolite NC-700 (Cardanol, meta-substituted alkenyl- Cardolitemono-phenol)

Preparation of a Toughness Improver (“D-1”)

150 g of poly-THF 2000 (OH number 57 mg/g KOH) and 150 of Liquiflex H(OH number 46 mg/g KOH) were dried at 105° C. under vacuum for 30minutes. When the temperature had been reduced to 90° C., 61.5 g of IPDIand 0.14 g of dibutyltin dilaurate were added. The reaction wascontinued at 90° C. under vacuum until the NCO content was constant at3.10% after 2.0 h (calculated NCO content: 3.15%). Then 96.1 g ofCardanol were added as a blocking agent. Stirring was continued at 105°C. under vacuum until the NCO content had dropped, after 3.5 h, below0.1%. The product in this form was used as toughness improver D-1.

Preparation of the Compositions

In accordance with the details in table 2, the reference compositionsRef. 1-Ref. 4 and also the inventive compositions 1, 2, 3, 4 and 5 wereprepared. In the reference examples there were in each case noaccelerant (Ref. 1) or accelerants not conforming to the formula (Ia)used, whereas this was the case for examples 1, 2, 3, 4 and 5. Theamount of accelerants used was calculated such that the overallconcentration of urea groups was constant.

Test Methods:

Tensile Shear Strength (TSS) (DIN EN 1465)

The specimens were produced from the above-described compositions andwith electrolytically galvanized DC04 steel (eloZn) with dimensions of100×25×0.8 mm, the bond area being 25×10 mm with a layer thickness of0.3 mm. Curing took place for 30 minutes at 180° C. (“TSS₁₈₀”), or for10 min at 165° C. (“TSS₁₆₅”), in a forced-air oven. Measurement tookplace after cooling to room temperature, after one day, with a pullingspeed of 10 mm/min.

Impact Peel Energy (ISO 11343)

The specimens were produced from the above-described compositions andwith electrolytically galvanized DC04 steel (eloZn) with dimensions of90×20×0.8 mm, the bond area being 20×30 mm with a layer thickness of 0.3mm. Curing took place for 30 minutes at 180° C. The impact peel energywas measured in each case at 23° C. The peeling speed was 2 m/s. Thefracture energy (“FE”) reported, in joules, is the area under themeasurement curve (from 25% to 90%, in accordance with ISO 11343).

As the increase in impact toughness relative to reference example Ref.1, the “Δ_(FE″)” value in the table was determined in accordance withthe following formula:

Δ_(FE)=[FE/FE(Ref. 1)]−1.

Viscosity

The adhesive samples were measured on a Bohlin CVO 120 plate/plateviscometer (diameter 25 mm, gap dimension 1 mm), frequency 5 Hz, 0.01deflection, temperature 23-53° C., 10° C./min. The viscosity in thiscase was determined as the complex viscosity at 25° C. from themeasurement plot.

Following their preparation, the adhesives were stored at 25° C. for 1day or at 60° C. for one week. After they had cooled to roomtemperature, the viscosity was measured, and was reported as “Visc (1 d,25° C.)”, or as “Visc (1 w, 60° C.)” in table 2. Viscosity increase(Δ_(visc)) was calculated in accordance with the formula

[Visc(1 w, 60° C.)/visc (1 d, 25° C.)]−1.

The results of these tests are summarized in table 2.

TABLE 2 Compositions and results. Ref. 1 Ref. 2 Ref. 3 Ref. 4 1 2 3 4 5DGEBA [pbw¹] 40.0 40.0 40.0 40.0 40.0 40.0 40.0 40.0 40.0 Polypox [pbw¹]3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 Polydis [pbw¹] 15.0 15.0 15.0 15.015.0 15.0 15.0 15.0 15.0 D-1 [pbw¹] 15.0 15.0 15.0 15.0 15.0 15.0 15.015.0 15.0 Dicy [pbw¹] 4.01 4.01 4.01 4.01 4.01 4.01 4.01 4.01 4.01TDIDMH [pbw¹] 0.51 TMH [pbw¹] 0.45 sym-DMH [pbw¹] 0.34 asym-DMH [pbw¹]0.34 BuDMH [pbw¹] 0.56 HDIDMH [pbw¹] 0.50 N100DMH [pbw¹] 0.79 BzDMH[pbw¹] 0.69 Filler mixture [pbw¹] 19.0 19.0 19.0 19.0 19.0 19.0 19.019.0 19.0 TTS₁₈₀ [MPa] 21.4 21.7 21.4 21.7 21.7 22.2 22.0 21.8 22.4TTS₁₆₅ [MPa] n.m.² 20.1 n.m.² n.m.² 19.8 21.2 21.1 21.0 21.1 FE [J] 14.216.1 13.9 14.4 16.5 17.5 17.4 16.3 17.3 Δ_(FE)[%] 13 −2 1 16 23 23 15 22Visc (1 d, 395 350 345 360 255 310 360 320 335 25° C.)[mPas] Visc (1 w,60° C.)[mPas] 395 1340 420 455 305 325 370 335 405 Δ_(visc) [%] 283 2226 20 5 3 5 21 ¹pbw = parts by weight ²n.m. = not measurable

The examples Ref. 1, Ref. 3, and Ref. 4 show such inadequate curing at165° that the specimens fell apart as early as during the removal of thefixing clamps following withdrawal from the oven; accordingly, it wasnot possible to measure a tensile shear strength. In these cases, theadhesive was still of low viscosity even after cooling to roomtemperature. Ref. 2, based on a urea with aromatic radicals, doesexhibit good cure behavior even at 165° C., but has a very low storagestability.

The inventive examples 1, 2, 3, 4, and 5 exhibit good mechanical valueseven after curing at 165° C., and also good storage stability.Furthermore, it is apparent from a comparison of examples Ref. 1 withRef. 4 or 1 that it is possible when using accelerants of the formula(Ia) in adhesives which already have a high degree of impact toughnessto achieve further sharp improvement in impact toughness, while this isnot the case for the corresponding aliphatic accelerants that do notconform to the formula (Ia). In the case of the aromatic accelerants(Ref. 2), it was in fact also possible to find this kind of increase inimpact toughness, but not to the same extent.

1. A heat-curing epoxy resin composition comprising a) at least oneepoxy resin A having on average more than one epoxide group permolecule; b) at least one epoxy-resin hardener B which is activated byelevated temperature and is an amine, amide, carboxylic anhydride orpolyphenol; and c) at least one accelerant C of the formula (Ia) or (Ib)

where R¹ is H or an n-valent aliphatic, cycloaliphatic or araliphaticradical; R² and R³ either each independently of one another are an alkylgroup or aralkyl group; or together are a divalent aliphatic radicalhaving 3 to 20 C atoms which is part of an optionally substitutedheterocyclic ring having 5 to 8; R^(1′) is an n′-valent aliphatic,cycloaliphatic or araliphatic radical; R^(2′) is an alkyl group oraralkyl group or alkylene group; R^(3′) independently at each occurrenceis H or an alkyl group or aralkyl group; and n and n′ are each from 1 to4.
 2. The heat-curing epoxy resin composition of claim 1, wherein theepoxy resin composition further comprises at least one toughnessimprover D.
 3. The heat-curing epoxy resin composition of claim 1,wherein n is 1 or
 2. 4. The heat-curing epoxy resin composition of claim1, wherein R¹ is H and R² and R³ are each a methyl, ethyl or propylgroup.
 5. The heat-curing epoxy resin composition of claim 1, wherein R¹alternatively is an alkylene group having 4 to 10 carbon atoms; or is

or is a biuret or an isocyanurate of an aliphatic or araliphaticdiisocyanate, following removal of the isocyanate groups; or is axylylene group.
 6. The heat-curing epoxy resin composition of claim 1,wherein the hardener B is selected from the group consisting ofdiaminodiphenol sulfone, adipic dihydrazide, trimellitic anhydridederivatives, novolaks, and dicyandiamide.
 7. The heat-curing epoxy resincomposition of claim 1, wherein the heat-curing epoxy resin compositionis free from organic carboxylic acids.
 8. The heat-curing epoxy resincomposition of claim 2, wherein the toughness improver D is selectedfrom the group consisting of blocked polyurethane polymers, liquidrubbers, epoxy resin-modified liquid rubbers, and core-shell polymers.9. The heat-curing epoxy resin composition of claim 2, wherein thetoughness improver D is a liquid rubber which is anacrylonitrile/butadiene copolymer terminated with carboxyl groups or(meth)acrylate groups or epoxide groups, or is a derivative thereof. 10.The heat-curing epoxy resin composition of claim 2, wherein thetoughness improver D is a blocked polyurethane polymer of the formula(II)

where Y¹ is a linear or branched polyurethane polymer PU1 terminatedwith m+m′ isocyanate groups, following the removal of all of theterminal isocyanate groups; Y² independently at each occurrence is ablocking group which is eliminated at a temperature above 100° C.; Y³independently at each occurrence is a group of the formula (II′)

where R⁴ is a radical of an aliphatic, cycloaliphatic, aromatic oraraliphatic epoxide, containing a primary or secondary hydroxyl groupfollowing the removal of the hydroxide groups and epoxide groups; p is1, 2 or 3 and m and m′ are each between 0 and 8, with the proviso thatm+m′ is from 2 to
 8. 11. The heat-curing epoxy resin composition ofclaim 9, wherein Y² is a radical which is selected from the groupconsisting of

where R⁵, R⁶, R⁷, and R⁸ each independently of one another is an alkylor cycloalkyl or aryl or aralkyl or arylalkyl group or R⁵ together withR⁶, or R⁷ together with R⁸, form part of a 4- to 7-membered ring whichif desired is substituted; R⁹, R^(9′) and R¹⁰ each independently of oneanother is an alkyl or aralkyl or aryl or arylalkyl group or is analkyloxy or aryloxy or aralkyloxy group; R^(H) is an alkyl group, R¹²,R¹³, and R¹⁴ each independently of one another are an alkylene grouphaving 2 to 5 C atoms, which optionally has double bonds or issubstituted, or are a phenylene group or a hydrogenated phenylene group;R¹⁵, R¹⁶, and R¹⁷ each independently of one another are H or are analkyl group or are an aryl group or an aralkyl group; and R¹⁸ is anaralkyl group or is a mono- or polycyclic substituted or unsubstitutedaromatic group which optionally contains aromatic hydroxyl groups. 12.The heat-curing epoxy resin composition of claim 10, wherein m is otherthan
 0. 13. The heat-curing epoxy resin composition of claim 1, whereinthe epoxy resin composition comprises at least one chemical blowingagent.
 14. The heat-curing epoxy resin composition of claim 1, whereinthat fraction of the epoxy resin A is 10%-85%.
 15. The heat-curing epoxyresin composition of claim 1, wherein the amount of the epoxy-resinhardener B which is activated by elevated temperature is 0.1%-30%. 16.The heat-curing epoxy resin composition of claim 1, wherein the amountof the accelerant C is 0.01%-6.0%.
 17. The heat-curing epoxy resincomposition of claim 2, wherein the fraction of the toughness improver Dis 0.1%-50%.
 18. A one-component heat-curing adhesive comprising theheat-curing epoxy resin composition of claim
 1. 19. A coating comprisingthe heat-curing epoxy resin composition of claim
 1. 20. A method forincreasing the impact toughness of heat-curing epoxy resin compositionscomprising adding an accelerant of the formula (Ia) or (Ib) as in claim1 to a heat-curing epoxy resin composition.
 21. A method of adhesivelybonding heat-stable materials, wherein these materials are contactedwith a heat-curing epoxy resin composition of claim 1 and the methodcomprises one or more steps of curing at a temperature of 100-220° C.22. The method of adhesive bonding of claim 21, wherein the materialsare contacted with heat-curing epoxy resin composition, after adhesivebonding, the adhesively bonded materials are used at temperaturesbetween 120° C. and −40° C.
 23. An adhesively bonded article obtained bya method of claim
 21. 24. The bonded article of claim 23, wherein thearticle is a vehicle or a component for installation in or on a vehicle.25. A structural foam for the reinforcement of cavities comprising theheat-curing epoxy resin composition of claim
 1. 26. A foamed articleobtained by at least partially filling a cavity with a heat-curingcomposition of claim 1 and heating the adhesively bonded materials to atemperature of 100-220° C.
 27. A vehicle or vehicle component comprisinga foamed article of claim 26.